Communication device and control method thereof

ABSTRACT

A communication device is provided in the present invention. The communication device comprises an oscillation signal source, a tunable capacitor array, a frame counter; and a control module. The control module is configured to jointly or separately control the tunable capacitor array and the frame counter to compensate a first frequency offset of the oscillation signal source when the communication device operates in a first mode, and to jointly or separately control the tunable capacitor array and the frame counter to compensate a second frequency offset of the oscillation signal source when the communication device operates in a second mode.

This application claims the benefit of U.S. provisional application Ser.No. 61/832,967, filed Jun. 10, 2013, the subject matter of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a frequency offset correctiontechnique for an oscillation signal source, and more particularly to atechnique for correcting a frequency offset of an oscillation signalsource caused by a loading amount.

2. Description of the Related Art

Most electronic systems are equipped with at least one oscillationsignal source (e.g., a crystal oscillator) that provides clock signalsas references for circuit operations. How to maintain a stable outputfrequency of an oscillation signal under all circumstances is animportant issue. For example, a frequency drift may arise in outputsignals of an oscillation signal source when an ambient temperaturechanges. To prevent functions of an electronic system from beingaffected by environmental factors, a frequency offset compensatingmechanism is essential in electronic systems.

Accompanied by advancements in electronic-related technologies, wirelesscommunication apparatuses in all diversities are becoming increasinglypopular. Circuits in current wireless communication apparatusesgenerally need two types of reference clock signals—system clock signalsand real-time clock signals. System clock signals have a higherfrequency (usually in MHz range), and are fundamental signals that manycircuits refer to for operations. Real-time clock signals have a lowerfrequency (usually in kHz range), and mainly serve for assisting awireless communication apparatus to count a real time (e.g., currenthour, minute and second) to facilitate the wireless communicationapparatus to synchronize and/or communicate with other wireless systemssuch as base stations. In a conventional hardware configuration, twosets of oscillation signal sources, having different oscillationfrequencies and respectively outputting system clock signals andreal-time signals, are arranged in the same wireless communicationapparatus.

To reduce hardware costs, in another conventional approach, system clocksignals and real-time clock signals are designed to share the sameoscillation signal source. FIG. 1 is an example showing a partialschematic diagram of such type of electronic system. In the example,system clock signals have a frequency of 26 MHz, and real-time clocksignals have a frequency of 32 kHz. The output frequency of anoscillation signal source 12 is 26 MHz and the output signal is providedto a buffer amplifier 14 and a frequency divider 16. The bufferamplifier 14 provides the amplified 26 MHz signals to its subsequentcircuits (e.g., a baseband circuit) to serve as system clock signals.The frequency divider 16 divides the 26 MHz signal to generate signalshaving a 32 kHz frequency. A frame counter 17, coupled to one of theoutputs of the frequency divider 16, counts the number of 32 kHz pulsesfrom the frequency divider 16, and changes its output signal when thecounting result reaches a predetermined threshold. The frame counter 17,which may be regarded as another frequency divider, outputs signals tocontrol the system events.

In practice, the electronic system in FIG. 1 may be a mobile phone. Inorder to have proper operations, the mobile phone has to be synchronizedto a base station which provides communication services. Thesynchronization is accomplished by decoding and tracking the differencebetween local clocks and the clocks in the base station. In the eventthat the clock signals of the mobile phone become inaccurate (e.g., whena frequency offset arises due to an ambient temperature change),settings of a coarse-tuning capacitor array 18A and/or a fine-tuningcapacitor array 18B may be adjusted (i.e., equivalent to changing aloading amount of the oscillation signal source 12) to correct theoutput frequency of the oscillation signal source 12.

It is well-known to those skilled in the art that a mobile phone entersfrom a normal operation mode to a low power consumption standby mode ata predetermined interval. To lower the overall power dissipation, in thelow power consumption mode, the buffer amplifier 14 and its subsequentcircuits that utilize the system clock signals are turned off. Thetuning capacitor arrays are set to their low capacitance state. It isapparent that the corresponding loading amounts that the oscillationsignal source 12 needs to drive are different between the normaloperation mode and the low power consumption mode. The change in theloading amount also causes a frequency offset in output signals of theoscillation signal source 12, leading the frequency of the real-timeclock signals to deviate from 32 kHz in the low power consumption mode.However, as the mobile phone in the low power consumption mode does notsynchronize with the base station, reference information for correctingthe frequency offset cannot be acquired. Thus, when the frequency offsetbecomes too excessive, the “real time” that is determined based on thereal-time clock signals may significantly deviate from the desired valuecausing the mobile phone to return to the normal operation mode eithertoo early or too late potentially failing the communication with a basestation.

SUMMARY OF THE INVENTION

The invention is directed to a communication device and frequency offsetcompensating method thereof for overcoming the above issues.

According to an embodiment of the present invention, a communicationdevice is provided. The communication device comprises an oscillationsignal source, a tunable capacitor array, a frame counter; and a controlmodule. The control module is configured to jointly or separatelycontrol the tunable capacitor array and the frame counter to compensatea first frequency offset of the oscillation signal source when thecommunication device operates in a first mode, and to jointly orseparately control the tunable capacitor array and the frame counter tocompensate a second frequency offset of the oscillation signal sourcewhen the communication device operates in a second mode.

According to another embodiment of the present invention, a controlmethod applied to a communication device is provided. The communicationdevice comprises an oscillation signal source, a tunable capacitor arrayand a frame counter. The control method comprises when the communicationdevice operates in a first mode, compensating a first frequency offsetof the oscillation signal source jointly or separately by the tunablecapacitor array and the frame counter; and when the communication deviceoperates in a second mode, compensating a second frequency offset of theoscillation signal source jointly or separately by the capacitor arrayand the frame counter.

The above and other aspects of the invention will become betterunderstood with regard to the following detailed description of thepreferred but non-limiting embodiments. The following description ismade with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example showing a partial schematic diagram of anelectronic system in which system clock signals and real-time clocksignals share a same oscillation signal source;

FIG. 2 is a function block diagram of an electronic system according toan embodiment of the present invention;

FIG. 3 is a detailed schematic diagram of compensation modules accordingto an embodiment of the present invention;

FIG. 4(A) and FIG. 4(B) illustrate corresponding relationships between acapacitor control code and a frequency offset compensation amount underdifferent modes; and

FIG. 5 is a flowchart of a frequency offset compensating methodaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a functional block diagram of an electronic systemaccording to an embodiment of the present invention. It should be notedthat, the term “present invention” refers to invention conceptsdescribed by embodiments below. However, the disclosed embodiments arenot to be construed as limitations to the scope of the inventionconcepts. In practice, for example, an electronic system 200 in FIG. 2may be a mobile communication device.

As shown in FIG. 2, the electronic system 200 includes an oscillationsignal source 21, a control module 22, a first compensation module 23, asecond compensation module 24, and a loading module 25. In practice, theloading module 25 may include one or multiple circuits that requireoscillation signals provided by the oscillation signal source 21 or canaffect the loading amount of the oscillation signal source 21. When theloading module 25 forms a first loading amount on the oscillation signalsource 21, the control module 22 jointly or separately controls thefirst compensation module 25 and the second compensation module 24 tocompensate a first frequency offset of the oscillation signal source 21caused by at least one environmental factor (e.g., a change in thetemperature and/or in a supply voltage). When the loading module 25changes from forming the first loading amount to forming a secondloading amount on the oscillation signal source 21, the control module22 jointly or separately controls the first compensation module 25 andthe second compensation module 24 to compensate a second frequencyoffset of the oscillation signal source 21 caused by a load difference.The load difference is a change between the first loading amount and thesecond loading amount. Operation details of the first compensationmodule 23 and the second compensation module 24 are to be describedshortly.

In practice, a change in the loading amount may occur when theelectronic system 200 changes its operation mode. For example, when theelectronic system 200 is switched from a normal operation mode to a lowpower consumption mode, a part of the circuits in the loading module 25and/or in the first compensation module 23 and/or in the secondcompensation module 24 may be partially disabled in a way that the totalloading amount seen by the oscillation signal source 21 is altered.Through simulations and experiments, the Applicant discovers that thefrequency offset of the oscillation signal caused by the change in theloading amount is substantially a fixed value, and does not fluctuatealong with the environmental factors such as the temperature. Therefore,the frequency offset caused by a change in the loading amount and thefrequency offset caused by the environmental factors may be jointly orseparately compensated by two different modules (the first compensationmodule 23 and the second compensation module 24).

In one embodiment, assume that a total load that the loading module 25and the compensation modules 23 and 24 form on the oscillation signalsource 21 when the electronic system 200 is in the normal operation modeis the foregoing first loading amount, and a total load that the loadingmodule 25 and the compensation modules 23 and 24 form on the oscillationsignal source 21 when the electronic system 200 is in the lower powerconsumption mode is the foregoing second loading amount. When theelectronic system 200 is in the normal operation mode, the frequencyoffset caused by the environmental factors are dynamically compensatedmainly by the first compensation module 23. In contrast, when theelectronic system 200 is switched from the normal operation mode to thelow power consumption mode, part of the first compensation module 23 andthe second compensation module 24 jointly or separately compensates thefrequency offset caused by the change in the loading amount. Inpractice, the total loading amount under different modes can bepredicted, and the frequency offset caused by the change in the loadingamount may be measured or calculated in advance before the electronicsystem 200 is shipped out of the factory. The information of thefrequency offset may be recorded in the control module 22, or berecorded in a storage device accessible by the control module 22 in theelectronic system 200 to accordingly control the first and the secondcompensation module 24 jointly or separately.

In one embodiment, the control module 22 supports an environmentalfactor detection function, and controls the first compensation module 23according to the detection result. In such circumstances, even when theelectronic system 200 is in the low power consumption mode, the firstcompensation module 23 may also compensate the frequency offset causedby the change in the environmental factors. In other words, the firstcompensation module 23 and the second compensation module 24 are capableof concurrent and independent operations.

When the electronic system 200 is a mobile communication device, thecontrol module 22 may determine the magnitude of an influence that theenvironmental factors pose on the oscillation signal source 21 accordingto reference data (e.g., time information) provided by a base station,and accordingly control the first compensation module 23 and determinethe amount of frequency compensation that the first compensation module23 is to apply to the oscillation signal source 21.

FIG. 3 shows a detailed schematic diagram of a first compensation module23 and the second compensation module 24 according to an embodiment. Asshown in FIG. 3, the first compensation module 23 may be a tunablecapacitor array, and includes a coarse-tune capacitor array 23A and afine-tune capacitor array 23B (to be jointly referred to as a capacitorarray 23). The second compensation module 24 is a frame counter. Theframe counter 24 counts the number of pulses in output signals from afrequency divider 25B, and changes its output signal when a countingresult reaches a predetermined threshold. Further, the loading module 25includes a buffer amplifier 25A and a frequency divider 25B. Outputfrequencies of the buffer amplifier 25A and the oscillation signalsource 21 are the same, and an output frequency of the frequency divider25B is lower than the output frequency of the oscillation signal source21. When the electronic system 200 is in the normal operation mode, thebuffer amplifier 25A and the frequency divider 25B are both maintainedin an operating state. When the electronic system 200 is in the lowpower consumption mode, the buffer amplifier 25A is turned off and partof the capacitor array 23 may be set to their low capacitance statewhereas the frequency divider 25B continues to operate.

A situation where the electronic system 200 is a mobile communicationdevice is described in embodiments below. Assume that when theelectronic system 200 is in the normal operation mode, the controlmodule 22 controls the capacitor array 23 according to the timeinformation provided by the base station to compensate the frequencyoffset caused by the change in the environmental factors. As theelectronic system 200 enters the low power consumption mode, theelectronic system 200 stops receiving the time information provided bythe base station, and the control module 22 however continues to controlthe capacitor array 23 according to the previously recorded frequencyoffset information to compensate the frequency offset caused by thechange in the environmental factors. On the other hand, assume that whenthe electronic system 200 is in the normal operation mode, the loadcontributed by the buffer amplifier 25A, the frequency divider 25B andthe capacitor array 23, and is seen by the oscillation signal source 21is a predetermined amount (a first loading amount). Thus, the controlmodule 22 adopts a predetermined counter threshold of the frame counter24; that is, the frequency offset caused by the change in the loadingamount need not be compensated. When the electronic system 200 is in thelow power consumption mode, the load contributed by the frequencydivider 25B and the capacitor array 23, and is seen by the oscillationsignal source 21 is different from the first loading amount, and is tobe referred to as a second loading amount. However, the foregoingassumptions are not to be construed as limitations of the scope of theinvention.

In one embodiment, when the electronic system 200 is switched from thenormal operation mode to the low power consumption mode, the controlmodule 22 continues utilizing a setting of the capacitor array 23 beforethe capacitor array 23 enters the low power consumption mode (i.e., thefrequency offset compensation amount that the capacitor array 23provides in the normal operation mode), and however changes the counterthreshold that the frame counter 24 adopts. One person skilled in theart of the technical field can appreciate that, for a subsequentcircuit, changing the counter threshold of the frame counter 24 isequivalent to changing an output signal frequency of the frequencydivider 25B, i.e., providing a frequency offset compensation amount. Aspreviously described, the frequency offset caused by the change in theloading amount due to turning off the buffer amplifier 25A and/or partof the capacitor array 23 may be measured in advance before theelectronic system 200 is shipped out of the factory. A circuit designermay accordingly estimate the amount of change to be made in the counterthreshold of the frame counter 24 in order to compensate the frequencyoffset caused by the change in the loading amount. In practice, thecounter thresholds corresponding to different modes may be stored in thecontrol module 22 in advance. When the electronic system 200 returns tothe normal operation mode, the control module 22 restores the counterthreshold of the frame counter 24 to a predetermined value (i.e.,terminating the frequency compensation function provided by the framecounter 24), and selectively tunes the capacitor array 23 againaccording to the time information provided by the base station.

In another embodiment, in the normal operation mode, the control module22 further records frequency offset information associated with theenvironmental factors, e.g., the amount of frequency offset caused bythe environmental factors, or a control code of the fine-tune capacitorarray 23B before entering the low power consumption mode. When theelectronic system 200 is switched from the normal operation mode to thelow power consumption mode, the setting before the capacitor array 23enters the low power consumption mode as in the previous embodiment isnot utilized. In this embodiment, after the electronic system 200 entersthe low power consumption mode, the control module 22 reducescapacitance values of the coarse-tune capacitor array 23A and thefine-tune capacitor array 23B (e.g., setting both of the coarse-tunecapacitor array 23A and the fine-tune capacitor array 23B to have aminimum capacitance value, such as zero). Since the capacitor array 23also affects the loading amount of the oscillation signal source 21 andcauses frequency offset on the oscillation signal source 21 when itssetting is changed, the capacitor array 23 can be regarded as a part ofthe loading module 25. In practice, as the change in the loading amountcaused by setting the capacitor array 23 to have a reduced capacitancevalue also causes a frequency offset, the control module 22correspondingly controls the frame counter 24 to further compensate thefrequency offset of the oscillation signal source 21 caused by thereduced capacitance value of the capacitor array 23. That is to say, inaddition to compensating the frequency offset caused by theenvironmental factors and turning off the buffer amplifier 25A, theframe counter 24 also compensates the frequency offset caused byreducing the capacitance value of the capacitor array 23. As previouslydescribed, the frequency offset caused by the environmental factors isrecorded by the control module 22 or learned from the control code ofthe fine-tune capacitor array 23B, the control module 22 may accordinglyestimate how to further adjust the counter threshold of the framecounter 24. More specifically, according to the control code of thecapacitor array 23 in the normal operation mode (i.e., before thereduction) and the control code of the capacitor array 23 in the lowpower consumption mode (i.e., after the reduction), the control module22 may learn a difference between before and after the reduction.According to a corresponding relationship between the control code ofthe capacitor array 23 and the frequency offset compensation amount, thecontrol module 22 obtains a frequency offset compensation amount toaccordingly adjust the counter threshold of the frame counter 24. Inpractice, the corresponding relationship between the control code of thecapacitor array 23 and the frequency offset compensation amount can bemeasured or calculated in advance and be recorded in the control module23 or the electronic system 200. An advantage of the above approach isthat, by reducing the capacitance values of the coarse-tune capacitorarray 23A and the fine-tune capacitor array 23B, the loading amount ofthe oscillation signal source 21 is lowered, accompanied by a loweredpower consumption. In other words, the above approach helps theelectronic system 200 to further lower the power consumption in the lowpower consumption mode, thereby prolonging the standby time of theelectronic system 200.

In another embodiment, when the electronic system 200 is switched fromthe normal operation mode to the low power consumption mode, the controlmodule 22 compensates the frequency offset caused by the change in theloading amount due to turning off the buffer amplifier 25A or part ofthe tuning capacitor array 23 (e.g., both of the coarse-tune capacitorarray 23A and the fine-tune capacitor array 23B are set to have aminimum capacitance value) by changing the counter threshold of theframe counter 24. There is still a residual frequency error due to thefinite resolution of the frame counter. However, given the low powerconsumption period of the electronic system 200 is not long in typicalsystems, the time deviation may be corrected according to the timedifference between the start of the local system event (e.g. enteringthe normal operation mode) and the time instance when the base stationstarts transmitting a paging signal to the system 200. For example, theelectronic system 200 needs to be switched from the low powerconsumption mode to the normal operation mode at time t, but theelectronic system 200 is switched to the normal operation mode at timet-x due to the time error. A counter may be used to count the timedifference between the time instance that the electronic system 200 isswitched to the normal operation mode and the time instance that theelectronic system 200 receives the paging signal from the base station.When the electronic system 200 receives the paging signal from the basestation at time t, the electronic system 200 can extract the timedifference x based on the counter. Such approach also helps theelectronic system 200 to lower the power consumption in the low powerconsumption mode.

In another embodiment, when the electronic system 200 is switch from thenormal operation mode to the low power consumption mode for the firsttime, the control module 22 compensates the frequency offset caused bythe change in the loading amount due to turning off the buffer amplifier25A or part of the capacitor array 23 to lower the power consumption bychanging the counter threshold of the frame counter 24. As previouslydescribed, as the electronic system 200 again enters the normaloperation mode, the control module 22 corrects the time error thatoccurred in a previous low power consumption period according to thetime difference between the time instance that the electronic system 200is switched to the normal operation mode and the time instance that theelectronic system 200 receives the paging signal from the base station.In this embodiment, the control module 22 further calculates thefrequency offset caused by the reduced capacitance value of thecapacitor array 23 according to the size of the time error, and utilizesthe calculated frequency offset as a frequency offset correction amount.Later, when the electronic system 200 is again switched from the normaloperation mode to the low power consumption mode, in addition tocompensating the frequency offset caused by the change in the loadingamount due to turning off the buffer amplifier 25A or part of thecapacitor array 23, the control module 22 controls the frame counter 24to also compensate the frequency offset estimated based on the timeerror according to the frequency offset correction amount.

In another embodiment, when the electronic system 200 is switched fromthe normal operation mode to the low power consumption mode for thefirst time, the control module 22 compensates the frequency offsetcaused by the change in the loading amount due to turning off the bufferamplifier 25A or part of the capacitor array 23 (e.g., setting both ofthe coarse-tune capacitor array 23A and the fine-tune capacitor array23B to have a minimum capacitance value such as zero) by changing thecounter threshold of the frame counter 24, That is to say, in additionto compensating the frequency offset caused by the change in the loadingamount due to turning off the buffer amplifier 25A or part of thecapacitor array 23, the frame counter 24 also compensates the frequencyoffset caused by the reduced capacitance value of the capacitor array23. Since the frequency offset can be learned from the control value ofthe capacitor array 23, the control module 22 may further estimate howto further adjust the counter threshold of the frame counter 24. Afterthe electronic system 200 again enters the normal operation mode, thecontrol module 22 may correct the time error that occurred in a previouslow power consumption period according to the time difference betweenthe time instance that the electronic system 200 is switched to thenormal operation mode and the time instance that the electronic system200 receives the paging signal from the base station. In thisembodiment, the control module 22 further obtains a frequency offsetcorrection amount according to the time error. Later, when theelectronic system 200 is again switched from the normal operation modeto the low power consumption mode, the control module 22 controls theframe counter 24 to further compensate the time error according to thefrequency offset correction amount.

In another embodiment, when the electronic system 200 is switched fromthe normal operation mode to the low power consumption mode, the controlmodule 22 compensates the frequency offset caused by the change in theloading amount due to turning off the buffer amplifier 25A or part ofthe capacitor array 23 by similarly changing the counter threshold ofthe frame counter 24, with however also changing the setting value ofthe capacitor array 23. In this embodiment, when the electronic system200 is switched from the normal operation mode to the low powerconsumption mode, the control module 22 sets the coarse-tune capacitorarray 23A to have a minimum capacitance value, and controls only thefine-tune capacitor array 23B to compensate the frequency offset causedby the environmental factors. In practice, as the change in the loadingamount caused by setting the coarse-tune capacitor 23A to have a minimumcapacitance value also causes a frequency offset, such frequency offsetis compensated by similarly changing the counter threshold of the framecounter 24. The loading amount that the coarse-tune capacitor array 23Ain different setting values forms on the oscillation signal source 21 isknown, and the frequency offset caused by the change in the loadingamount can also be measured or calculated in advance before theelectronic system 200 is shipped out of the factory. The frequencyoffset information may be recorded in the control module 22, or berecorded in a storage device accessible by the control module 22 in theelectronic system 200. The control module 22 may control the framecounter 24 according to the frequency offset information to performcompensation. In practice, when the coarse-tune capacitor array 23A isset to have a minimum capacitance value, due to a change in the overallloading structure, the corresponding relationship between the settingvalue of the fine-tune capacitor array 23B and the frequency offsetcompensation amount is also changed, as shown by an example in FIG.4(A).

In FIG. 4(A), the horizontal-axis coordinate represents the control codecorresponding to the capacitance value of capacitance array 23B; thecapacitance value gets larger as the control code gets larger. In FIG.4(A), the vertical-axis coordinate represents the frequency offsetcompensation amount. In this example, the fine-tune capacitor array 23Bis designed to provide a frequency offset compensation value of −80ppm˜+80 ppm (the first curve) under the normal operation mode. As shownin FIG. 4(A), when the coarse-tune capacitor array 23A is set to havethe minimum capacitance value, the frequency offset compensation amountthat the fine-tune capacitor array 23B can provide becomes −160 ppm˜+160ppm (the second curve). Therefore, in the low power consumption mode,the control module 22 needs to change the control code of the fine-tunecapacitor array 23B according to the new corresponding relationship. Forexample, to provide the same frequency offset compensation amount of +40ppm, the control code of the fine-tune capacitor array 23B in the normaloperation mode is 256 and may change to 384 in the low power consumptionmode. To have the fine-tune capacitor array 23B provide a frequencyoffset compensation amount of −80ppm˜+80 ppm in the low powerconsumption mode, the fine-tune capacitor array 23 having a control codebetween 256 and 768 is sufficient. It should be noted that, thecorresponding relationship between the control code of the fine-tunecapacitor array 23 and the frequency offset compensation amount can bemeasured or calculated in advance. Taking FIG. 4(A) for example, beforethe electronic system 200 is shipped out of the factory, on the basisthat the control code of the fine-tune capacitor array 23B is 512, aslope of the first curve (the normal operation mode) and a slope of thesecond curve (the low power consumption mode) are measured, and theslopes and the control code of the fine-tune capacitor array 23B servingas references are recorded. It should be noted that, the measurement andcalculation for the corresponding relationship are known to one personskilled in the art, and shall be omitted herein.

In another embodiment, as shown in FIG. 4(B), when the control code is0, the fine-tune capacitor array 23B provides a frequency offsetcompensation amount of +80 ppm. In this example, to have the fine-tunecapacitor array 23B provide a frequency offset compensation amount of−80 ppm˜+80 ppm in the low power consumption mode, the fine-tunecapacitor array 23B having a control code between 0 to 512 is sufficientto thus further lower the power consumption of the electronic system200. In practice, before the electronic system 200 is shipped out of thefactory, on the basis that the control code of the fine-tune capacitorarray 23B is 0, the slope of the first curve (the normal operation mode)and the slope of the second curve (the low power consumption mode) aremeasured, and the slopes and the control code of the fine-tune capacitorarray 23B serving as references are recorded. As such, the correspondingrelationship between the control code of the fine-tune capacitor array23B and the frequency offset compensation amount shown in FIG. 4(B) canbe obtained.

According to another embodiment of the present invention, a frequencyoffset compensating method applied to an electronic system is provided.FIG. 5 shows a flowchart of the frequency offset compensating method.The electronic system includes an oscillation signal source, a loadingmodule, a first compensation module, and a second compensation module.In step S51, when the loading module forms a first loading amount on theoscillation signal source, the first and second compensation modules arejointly or separately controlled to compensate a first frequency offsetof the oscillation signal source caused by at least one environmentalfactor with a first setting. In step S52, when the loading modulechanges from forming the first loading amount to forming a secondloading amount on the oscillation signal source, the first and secondcompensation modules are jointly or separately controlled to compensatea second frequency offset of the oscillation signal source caused by aloading difference with a second setting. The loading difference is adifference between the first loading amount and the second loadingamount. One person skilled in the art can understand that, variousoperations and modifications in the description associated with theelectronic system 200 are applicable to the frequency offsetcompensating method in FIG. 5, and shall be omitted herein.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited thereto. On the contrary, it is intended to cover variousmodifications and similar arrangements and procedures, and the scope ofthe appended claims therefore should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements and procedures.

What is claimed is:
 1. A control method, applied to a communicationdevice comprising an oscillation signal source, a tunable capacitorarray and a frame counter, the control method comprising: when thecommunication device operates in a first mode, compensating a firstfrequency offset of the oscillation signal source jointly or separatelyby the tunable capacitor array and the frame counter; and when thecommunication device operates in a second mode, compensating a secondfrequency offset of the oscillation signal source jointly or separatelyby the tunable capacitor array and the frame counter.
 2. The controlmethod according to claim 1, further comprising: providing predeterminedcompensation information; wherein, the frame counter compensates thesecond frequency offset of the oscillation signal source according tothe predetermined compensation information.
 3. The control methodaccording to claim 1, further comprising: when the communication deviceis switched from the first mode to the second mode, reducing acapacitance value of the tunable capacitor array.
 4. The control methodaccording to claim 3, wherein when the communication device operates inthe second mode, the frame counter compensates the second frequencyoffset of the oscillation signal source according to a control value ofthe tunable capacitor array.
 5. The control method according to claim 1,further comprising: determining correction information according to atime difference between the time instance that the communication deviceis switched to the first mode and the time instance that thecommunication device receives a paging signal from a base station;wherein, when the communication device operates in the second mode, theframe counter compensates the second frequency offset of the oscillationsignal source according to the correction information.
 6. The controlmethod according to claim 1, wherein the first frequency offset iscaused by at least one environmental factor, which comprises atemperature factor or a power supply factor.
 7. The control methodaccording to claim 6, wherein the tunable capacitor array comprises acoarse-tune capacitor array and a fine-tune capacitor array; the controlmethod further comprising: when the communication device operates in thesecond mode, compensating the first frequency offset of the oscillationsignal source by the frame counter according to a setting value of thefine-tune capacitor array before entering the second mode.
 8. Thecontrol method according to claim 6, wherein the tunable capacitor arraycomprises a coarse-tune capacitor array and a fine-tune capacitor array;the control method further comprising: reducing a capacitance value ofthe coarse-tune capacitor array and correspondingly changing a settingvalue of the fine-tune capacitor array to compensate the first frequencyoffset.
 9. The control method according to claim 8, wherein when thecommunication device operates in the second mode, the frame countercompensates the second frequency offset of the oscillation signal sourceaccording to a setting value of the coarse-tune capacitor array.
 10. Acommunication device, comprising: an oscillation signal source; atunable capacitor array; a frame counter; and a control module,configured to jointly or separately control the tunable capacitor arrayand the frame counter to compensate a first frequency offset of theoscillation signal source when the communication device operates in afirst mode, and to jointly or separately control the tunable capacitorarray and the frame counter to compensate a second frequency offset ofthe oscillation signal source when the communication device operates ina second mode.
 11. The communication device according to claim 10,wherein the control module controls the frame counter to compensate thesecond frequency offset of the oscillation signal source according topredetermined compensation information.
 12. The communication deviceaccording to claim 10, wherein the control module reduces a capacitancevalue of the tunable capacitor array when the communication device isswitched from the first mode to the second mode.
 13. The communicationdevice according to claim 12, wherein when the communication deviceoperates in the second mode, the frame counter compensates the secondfrequency offset of the oscillation signal source according to a controlvalue of the tunable capacitor array.
 14. The communication deviceaccording to claim 10, wherein the control module determines correctioninformation according to a time difference between the time instancethat the communication device is switched to the first mode and the timeinstance that the communication device receives a paging signal from abase station, and controls the frame counter to compensate the secondfrequency offset of the oscillation signal source according to thecorrection information when the communication device operates in thesecond mode.
 15. The communication device according to claim 10, whereinthe first frequency offset is caused by at least one environmentalfactor, which comprises a temperature factor or a power supply factor.16. The communication device according to claim 15, wherein the tunablecapacitor array comprises a coarse-tune capacitor array and a fine-tunecapacitor array, and when the communication device operates in thesecond mode, the frame counter compensates the first frequency offset ofthe oscillation signal source according to a setting value of thefine-tune capacitor array before entering the second mode.
 17. Thecommunication device according to claim 15, wherein the tunablecapacitor array comprises a coarse-tune capacitor array and a fine-tunecapacitor array, and the control module reduces a capacitance value ofthe coarse-tune capacitor array and correspondingly changes a settingvalue of the fine-tune capacitor array to compensate the first frequencyoffset.
 18. The communication device according to claim 17, wherein whenthe communication device operates in the second mode, the frame countercompensates the second frequency offset of the oscillation signal sourceaccording to a setting value of the coarse-tune capacitor array.